Transparent shields of the type to be worn in front of the face, especially designed to be attached to safety helmets for motorcycle riders, to so-called hard hats for workers, or to mounting rings or mounting straps worn on the head, are usually made of polycarbonate or cellulose acetate. These plastics have the considerable advantage that they are flexible, i.e., the shield is stamped out of a sheet and can then be bent to the shape of a helmet, and that they do not shatter when struck. On the other hand, they have the considerable disadvantage that they are not scratch-resistant. In practice, the shields of safety helmets worn by motorcycle riders of workers' hard hats very quickly become dirty. The only possibility for the wearer to effect at least partial cleaning during riding or during work involves wiping off the shield with his bare hand or with a glove, i.e., dry-wiping it; in a short time this results in scratching of the shield, making it unusable. In the case of shields for motorcycle riders, because of this problem, it has been proposed that a portion of the transparent shield be made interchangeable, with this interchangeable part being made of the same material as the shield. This design has not managed to become general.
It is known from U.S. Pat. No. 3,377,625 to provide ski goggles with a so-called double shield; both of these shields are sealed tightly together, thus preventing fogging of the inside of the inner shield due to the high insulating properties. The double shield in any case is made of a homogeneous material.